The present invention relates to a power supply device for low-voltage electronic residual current circuit breakers (RCCBs) and the like.
In particular, the power supply device, according to the present invention, is suitable for use in electronic RCCBs for applications of the single-phase or multiple-phase (two-phase, three-phase, et cetera) with operating voltages around 1000 V or less.
Many examples of low-voltage electronic RCCBs are known in the background art.
The structure of a low-voltage electronic RCCB of the known type is illustrated schematically with reference to FIG. 1.
In general, a low-voltage electronic RCCB, designated by the reference numeral 1, comprises a sensor 2, which is suitable to generate a signal 3, indicative of the presence of an imbalance current due to a ground-fault, in an electrical network 4 of the single- or multi-phase type.
The signal 3 is received in input by an electronic protection system 5, which generates control signals 6 in order to drive, for example, an electromagnetic release device and/or electronic signaling devices or auxiliary electronic devices (reference 8), aimed at providing signals related to the status of the apparatus or circuit breaker.
The electronic protection system 5, the electromagnetic release 7 and the signaling devices 8 must, for their correct operation, be supplied with a given electrical power level PAL, generally provided by an electronic power supply device 9, which has in output a power supply voltage VAL.
Traditionally, the electronic power supply device 9 can be realized according to different approaches.
According to a first constructive approach, the electronic power supply device 9 is structured, so as to receive electrical power (dashed arrow 10) directly from the sensor 2, which is used to detect the vector imbalance of the currents, between the phases of the electrical network 4. This type of approach, which offers the unquestionable advantage of ensuring power supply (and consequently operation of the RCCB) in a manner virtually independent of the mains voltage, has considerable drawbacks. In fact, the electrical power PAL that can be made available by the power supply device 9 is generally reduced (a few hundred mVA) and allows to supply an electronic protection system 5 or an electromagnetic release 7, which have to be necessarily of the low-power type. It also becomes difficult to supply power to other devices, which are accessories or are of the auxiliary type. Thus, one can say that the power supply devices 9, provided according to the first type of approach described, are often affected by considerable operating limitations.
In an alternative constructive approach, the electronic power supply device 9 is structured so as to obtain electric power (dashed arrow 11) directly from the electrical network 4. In order to be able to supply the electric power PAL, voltages and currents (VIN and IIN) of the phases of the electric network 4 are made available by means of a rectifier bridge and an appropriate network of resistive and capacitive passive elements (not shown). A network of passive elements of the nonlinear type 12 is generally used in order to widen the available range of the input supply voltage.
Practice has shown that also this constructive approach has considerable drawbacks, even though it is inherently very robust and capable of costantly supplying an adequate power level PAL.
The use of a network of passive elements makes it difficult to ensure that a stable power supply condition is reached with a low transient period, when supply voltage ranges very different from each other have to be adopted.
Furthermore, in this case, it is necessary to dissipate as heat the excess available energy for the higher supply voltage ranges.
Moreover, the use of nonlinear passive components is very often critical, since these components generally have relatively large size and considerably high costs, in comparison with the costs of commonly used active or passive circuit elements.
Additionally, owing to the need to optimize the working point of the electrical network of passive elements, according to the supplied electric power, it is often necessary to provide a different type of power supply device 9 for each different supply voltage range, which has to be supplied.
For these reasons, the practice has shown that, often, the use of power supply devices of this type is scarcely flexible, leading to a consequent increase in production costs, installation costs and operating costs of the electronic RCCB.